This invention relates to the field of electronic timers, and more particularly to the field of electronic elapsed time meters for vehicles and other motorized equipment and analogous or equivalent applications requiring maintenance at periodic intervals.
At present, there is a need in commerce and industry for a compact, inexpensive and accurate, electronic digital time meter for measuring, over a period of months or years and through intermittent power outages on a motorized vehicle or piece of equipment, the total time a monitored signal is present. For example, on a forklift truck in a warehouse, or a motor-generator set in a factory, it would be useful to monitor the total time the vehicle or equipment is running, or performing some particular function.
Persons needing such a time meter include maintenance personnel who perform preventive maintenance on such vehicles or equipment at regularly scheduled intervals determined by actual time the vehicle or equipment has been in use.
Those who might well desire such a timer include supervisory personnel who wish to record the amount of time drivers of vehicles are performing a particular task, industrial engineers studying and measuring the efficiencies of various man-vehicle combinations, and maintenance personnel troubleshooting problems with the vehicles, motor-generator sets, or other motorized equipment that operates intermittently.
For certain applications of such time meters, it would be desirable or even necessary to make the digitial display of the meter detachable, that is, easily and manually removable. Removing the display would prevent unauthorized reading of the meter and protect the display from physical damage. Also, the total cost of several meters used as a set could be reduced by such a feature since one display could be employed to read all of the meters in the set.
In other applications, it may be desirable or required to have a meter whose internal battery could be replaced without interrupting the timing or totalizing functions of the meter.
Certain applications of such a meter may require a means for comparing the total elapsed time measured by the meter against a preset value and sounding an alarm or disabling a function on the vehicle or equipment when the elapsed time equals or exceeds the preset value. This feature could be used to assure that appropriate action is taken with respect to the vehicle or equipment being monitored at prescribed intervals.
Traditionally, electronic digital timers have not been used to measure intermittent signals over a period of several months or years. One of the primary reasons for this is that an unacceptably large internal battery would have been required to operate a traditional timing circuit made of discrete components over such an extended period. Also, the large number of discrete components traditionally required in such an electronic timer would have made it prohibitively expensive and large in comparison to an electro-mechanical timer or a timer employing a coulometric electrolytic cell for integration elapsed time. Advancements in integrated circuit technology in the past decade have reduced the size, power comsumption and cost of timing circuits and digital display circuits and digital display circuits to the point where electronic digital time meters are now practical and cost-competitive, providing inventors with the incentive to turn their attention to this area.
The basic object of this invention is to provide a digital time meter adapted for measuring and time-totalizing an intermittent electrically monitorable condition or signal on motorized commercial or industrial equipment over a period of several months or years without changing the battery within the meter.
Another object of this invention is to provide a digital time meter adapted for fulfilling the basic object of this invention with excellent accuracy.
Still another object of this invention is to provide a digital time meter with a removable display.
Still another object of this invention is to provide a digital time meter whose battery can be replaced without resetting or interrupting the timing function of the meter.
Yet another object of this invention is to provide a digital time meter having a means for providing an alarm or signaling external equipment when the accumulated time on the meter equals or exceeds a preset value stored within the meter.
Other objects, features and advantages of the present invention will become apparent from the subsequent description and the appended claims, taken in conjunction with the accompanying drawings.